The present disclosure relates to a storage element that includes a storage layer storing a magnetization state of a ferromagnetic layer as information and a magnetization fixing layer in which the direction of magnetization is fixed and the direction of the magnetization of the storage layer is changed by causing a current to flow, and a storage device including the storage element.
With rapid development of various information apparatuses such as mobile terminals and large-capacity servers, new high performance features such as high integration, high speed, and low power consumption have been studied on elements such as memories or logic circuits included in various information apparatuses. In particular, semiconductor non-volatile memories have been highly advanced and flash memories such as high-capacity file memories have been proliferated as hard disk drives. On the other hand, development of ferroelectric random access memories (FeRAMs), magnetic random access memories (MRAMs), phase-change random access memories (PCRAMs), and the like is in progress to develop these memories to code storages or working memories and to substitute the currently available NOR flash memories or DRAMs. Moreover, some of the memories have already been put to practical use.
Of the memories, MRAMs are capable of rewriting data rapidly and almost infinitely (more than 1015 times) because data is stored according to a direction of magnetization of a magnetic body, and have already been used in fields of industry automation, airplanes, or the like. MRAMs are expected to be developed into code storages or working memories in the future in terms of a high speed operation and reliability. In reality, difficulties of low power consumption and large capacity have become a problem. This problem is an inherent problem with a recording principle of MRAMs, that is, a method of causing a current to flow in two kinds of address lines (a word line and a bit line) substantially perpendicular to one another and recording information by reversing the magnetization of a magnetic layer of a magnetic storage element at an intersection of the address lines using a current magnetic field generated from each address line, that is, reversing the magnetization using the current magnetic field generated from each address line.
As one of the solutions to this problem, recording types performed without dependency on the current magnetic field, that is, magnetization reversing types, have been examined. Of these types, studies on spin torque magnetization reversal have actively been made (for example, see Japanese Unexamined Patent Application Publication No. 2003-17782, U.S. Pat. No. 6,256,223, Japanese Unexamined Patent Application Publication No. 2008-227388, Phys. Rev. B 54, 9353 (1996), and J. Magn. Mat., 159, Li (1996)).
The spin torque magnetization reversal type storage elements are configured by a magnetic tunnel junction (MTJ), as in MRAMs, in many cases. In such a configuration, a free magnetic layer is reversed when a current with a value equal to or greater than a given threshold is caused to flow by applying a torque (which is called a spin transfer torque) to a magnetic layer when spin-polarized electrons passing through the magnetic layer fixed in a given direction enter another free magnetic layer (in which a direction is not fixed). Rewriting “0/1” is performed by changing the polarity of the current.
An absolute value of the current used to reverse the magnetic layer is 1 mA or less in an element with a scale of about 0.1 μm. Further, scaling can be performed to decrease the current value in proportion to an element volume. Furthermore, there is an advantage of simplifying a cell structure, since a recording current magnetic field generation word line, which is necessary in MRAMs, is not necessary.
Hereinafter, an MRAM using spin torque magnetization reversal is referred to as a spin torque-magnetic random access memory (ST-MRAM). The spin torque magnetization reversal is also referred to as spin injection magnetization reversal. An ST-RAM is highly expected to be realized as a non-volatile memory that has the advantages of low power consumption and large capacity in addition to the advantages of an MRAM in which data is rewritten rapidly and almost infinitely.